Base station and user terminal

ABSTRACT

A base station according to a first aspect allocates a gap pattern to a user terminal connected to an own cell based on a message received from the user terminal, the gap pattern defines timings in which the user terminal should monitor D2D signals transmitted from other user terminals at different frequencies than a frequency of the own cell. The base station includes a transmitter that transmits feedback control information to the user terminal, the feedback control information used to determine whether or not it is necessary for the user terminal to include, in the message, feedback corresponding to system information that is received by the user terminal at the different frequencies.

TECHNICAL FIELD

The present invention relates to a base station and a user terminal usedin a mobile communication system in which a D2D proximity service issupported.

BACKGROUND ART

In the 3rd Generation Partnership Project (3GPP) that is a mobilecommunication system standardization project, introduction of adevice-to-device (D2D) proximity service as a new function after Release12 is under review (see Non Patent Literature 1).

The D2D proximity service (D2D ProSe) is a service that enables directD2D communication to be performed in a synchronous cluster including aplurality of user terminals which are synchronized with one another. TheD2D proximity service includes a D2D discovery process (ProSe Discovery)of discovering a nearby terminal and D2D communication (ProSeCommunication) that is direct D2D communication.

Here, a serving cell can notify a user terminal of another frequencythat supports the D2D proximity service and is different from afrequency of the serving cell through system information (a systeminformation block (SIB)). The user terminal may monitor a D2D signalthat is transmitted at another frequency that is notified of through theSIB.

CITATION LIST Non Patent Literature

Non Patent Literature 1: 3GPP Technical Report “TR 36.843 V12.0.1,” Mar.27, 2014

SUMMARY OF INVENTION

Meanwhile, time/frequency resources (D2D resource pool) used fortransmission of the D2D signal are assumed to be set to a specific timezone delimited by a predetermined period of time other than all timezones.

The user terminal receives a notification of another frequency at whichthe D2D proximity service is supported from the serving cell but doesnot receive a notification of the D2D resource pool used fortransmission of the D2D signal from the serving cell.

Further, it is commonly difficult for the user terminal to performmonitoring of the D2D signal and cellular communication at the sametime, and thus it is desirable that the D2D signal that is transmittedat another frequency can be appropriately monitored.

In this regard, the objective of the present invention is to provide abase station and a user terminal, which are capable of appropriatelymonitoring the D2D signal transmitted at another frequency differentfrom the frequency of the serving cell.

A base station according to a first aspect allocates a gap pattern to auser terminal connected to an own cell based on a message received fromthe user terminal, the gap pattern defines timings in which the userterminal should monitor D2D signals transmitted from other userterminals at different frequencies than a frequency of the own cell. Thebase station includes a transmitter that transmits feedback controlinformation to the user terminal, the feedback control information usedto determine whether or not it is necessary for the user terminal toinclude, in the message, feedback corresponding to system informationthat is received by the user terminal at the different frequencies.

A user terminal according to a second aspect is a terminal to which agap pattern is allocated by a serving cell based on a messagetransmitted to the serving cell, the gap pattern defines timings inwhich the user terminal should monitor D2D signals transmitted fromother user terminals at different frequencies than a frequency of theserving cell. The user terminal includes a receiver that receivesfeedback control information from the serving cell, the feedback controlinformation used to determine whether or not it is necessary for theuser terminal to include, in the message, feedback corresponding tosystem information that is received by the user terminal at thedifferent frequencies.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating an LTE system.

FIG. 2 is a block diagram illustrating a UE (user terminal).

FIG. 3 is a block diagram illustrating an eNB (base station).

FIG. 4 is a protocol stack diagram of a radio interface in an LTEsystem.

FIG. 5 is a configuration diagram illustrating a radio frame used in anLTE system.

FIG. 6 is a diagram for describing inter-frequency discovery accordingto an embodiment.

FIG. 7 is a diagram for describing monitoring gap allocation accordingto an embodiment.

FIGS. 8(a) to 8(d) are diagrams for describing an exemplaryconfiguration of a requested gap pattern according to an embodiment.

FIG. 9 is a diagram for describing feedback control according to anembodiment.

DESCRIPTION OF EMBODIMENTS Overview of Embodiment

A base station according to a first aspect allocates a gap pattern to auser terminal connected to an own cell based on a message received fromthe user terminal, the gap pattern defines timings in which the userterminal should monitor D2D signals transmitted from other userterminals at different frequencies than a frequency of the own cell. Thebase station includes a transmitter that transmits feedback controlinformation to the user terminal, the feedback control information usedto determine whether or not it is necessary for the user terminal toinclude, in the message, feedback corresponding to system informationthat is received by the user terminal at the different frequencies.

In an embodiment, the system information includes resource poolinformation indicating a D2D resource pool used for transmission of theD2D signals at the different frequencies. The feedback is a requestedgap pattern that is decided by the user terminal based on the resourcepool information, or the resource pool information.

In an embodiment, the feedback control information includes informationindicating whether or not the feedback is necessary.

In an embodiment, the system information includes a tag number that isupdated with an update of the system information. The feedback controlinformation includes the tag number of the system information acquiredby the base station in order for the user terminal to determine whetherthe feedback is necessary.

In an embodiment, the feedback control information includes informationindicating a gap pattern acquired by the base station in order for theuser terminal to determine whether the feedback is necessary.

In an embodiment, the feedback control information is provided for eachfrequency included in the different frequencies.

In an embodiment, the feedback control information includes informationindicating a valid period of time of the feedback control information.

A user terminal according to a second aspect is a terminal to which agap pattern is allocated by a serving cell based on a messagetransmitted to the serving cell, the gap pattern defines timings inwhich the user terminal should monitor D2D signals transmitted fromother user terminals at different frequencies than a frequency of theserving cell. The user terminal includes a receiver that receivesfeedback control information from the serving cell, the feedback controlinformation used to determine whether or not it is necessary for theuser terminal to include, in the message, feedback corresponding tosystem information that is received by the user terminal at thedifferent frequencies.

In an embodiment, the system information includes resource poolinformation indicating a D2D resource pool used for transmission of theD2D signals at the different frequencies. The feedback is a requestedgap pattern that is decided by the user terminal based on the resourcepool information, or the resource pool information.

In an embodiment, the feedback control information includes informationindicating whether or not the feedback is necessary.

In an embodiment, the system information includes a tag number that isupdated with an update of the system information. The feedback controlinformation includes the tag number of the system information acquiredby the base station in order for the user terminal to determine whetherthe feedback is necessary.

In an embodiment, the feedback control information includes informationindicating a gap pattern acquired by the base station in order for theuser terminal to determine whether the feedback is necessary.

In an embodiment, the feedback control information is provided for eachfrequency included in the different frequencies.

In an embodiment, the feedback control information includes informationindicating a valid period of time of the feedback control information.

Embodiments

Hereinafter, an embodiment for a case where the present invention isapplied to an LTE system will be explained.

(System Configuration)

Hereinafter, the system configuration of the LTE system according to anembodiment will be explained. FIG. 1 is a configuration diagram of theLTE system according to the embodiment. As illustrated in FIG. 1, theLTE system according to the embodiment includes UE (User Equipment) 100,E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 10, and EPC(Evolved Packet Core) 20.

The UE 100 corresponds to a user terminal. The UE 100 is a mobilecommunication device, which performs radio communication with a cell (aserving cell). The configuration of the UE 100 will be described later.

The E-UTRAN 10 corresponds to a radio access network. The E-UTRAN 10includes an eNB 200 (evolved Node-B). The eNB 200 corresponds to a basestation. The eNBs 200 are connected mutually via an X2 interface. Theconfiguration of the eNB 200 will be described later.

The eNB 200 manages one or a plurality of cells, and performs radiocommunication with the UE 100 that establishes a connection with a cellof the eNB 200. The eNB 200 has a radio resource management (RRM)function, a routing function of user data, a measurement controlfunction for mobility control and scheduling and the like. The “cell” isused as a term indicating a smallest unit of a radio communication area,and is also used as a term indicating a function of performing radiocommunication with the UE 100.

The EPC 20 corresponds to a core network. The network of LTE system isconfigured by the E-UTRAN 10 and the EPC 20. The EPC 20 includes an MME(Mobility Management Entity)/S-GW (Serving-Gateway) 300. The MMEperforms different types of mobility control and the like for the UE100. The S-GW performs transfer control of the user data. The MME/S-GW300 is connected to the eNB 200 via an S1 interface.

FIG. 2 is a block diagram of the UE 100. As illustrated in FIG. 2, theUE 100 includes an antenna 101, a radio transceiver 110, a userinterface 120, a GNSS (global navigation satellite system) receiver 130,a battery 140, a memory 150, and a processor 160. The memory 150corresponds to a storage, and the processor 160 corresponds to acontroller. The UE 100 may not have the GNSS receiver 130. The memory150 may be integrally formed with the processor 160, and this set (thatis, a chip set) forming the controller may be called a processor 160′.

The antenna 101 and the radio transceiver 110 are used to transmit andreceive a radio signal. The radio transceiver 110 converts a basebandsignal (a transmission signal) output from the processor 160 into theradio signal and transmits the radio signal from the antenna 101.Furthermore, the radio transceiver 110 converts a radio signal receivedby the antenna 101 into a baseband signal (a received signal), andoutputs the baseband signal to the processor 160. The radio transceiver110 and the processor 160 form a transmitter and a receiver.

The radio transceiver 110 may plural transmitters and/or pluralreceivers. In an embodiment, a case where the transceiver 110 includes atransmitter and a receiver is assumed.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, variousbuttons and the like. The user interface 120 receives an operation froma user and outputs a signal indicating the content of the operation tothe processor 160. The battery 140 accumulates a power to be supplied toeach block of the UE 100. If the UE 100 is a card-type-terminal, the UE100 may not include the user interface 120 and the battery 140.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for processing by the processor 160. Theprocessor 160 includes a baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signal,and a CPU (Central Processing Unit) that performs various processes byexecuting the program stored in the memory 150. The processor 160 mayfurther include a codec that performs encoding and decoding on sound andvideo signals. The processor 160 executes various types of processes andvarious communication protocols described later.

FIG. 3 is a block diagram of the eNB 200. As illustrated in FIG. 3, theeNB 200 includes an antenna 201, a radio transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230corresponds to a storage, and the processor 240 corresponds to acontroller. Furthermore, the memory 230 may be integrally formed withthe processor 240, and this set (that is, a chipset) forming thecontroller may be called a processor 240′.

The antenna 201 and the radio transceiver 210 are used to transmit andreceive a radio signal. The radio transceiver 210 converts a basebandsignal (a transmission signal) output from the processor 240 into theradio signal and transmits the radio signal from the antenna 201.Furthermore, the radio transmitter 210 converts a radio signal receivedby the antenna 201 into a baseband signal (a received signal), andoutputs the baseband signal to the processor 240. The radio transceiver210 and the processor 240 form a transmitter and a receiver.

The network interface 220 is connected to the neighboring eNB 200 viathe X2 interface and is connected to the MME/S-GW 300 via the S1interface. The network interface 220 is used in communication performedon the X2 interface and communication performed on the S1 interface.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for processing by the processor 240. Theprocessor 240 includes a baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 executes various types ofprocesses and various communication protocols described later.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem. As shown in FIG. 4, the radio interface protocol is classifiedinto a first layer to a third layer of an OSI reference model, such thatthe first layer is a physical (PHY) layer. The second layer includes aMAC (Medium Access Control) layer, an RLC (Radio Link Control) layer,and a PDCP (Packet Data Convergence Protocol) layer. The third layerincludes an RRC (Radio Resource Control) layer.

The physical layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the physical layer of the UE 100 and the physicallayer of the eNB 200, user data and control signals are transmitted viaa physical channel.

The MAC layer performs priority control of data, a retransmissionprocess by a hybrid ARQ (HARQ) and the like. Between the MAC layer ofthe UE 100 and the MAC layer of the eNB 200, user data and controlsignals are transmitted via a transport channel. The MAC layer of theeNB 200 includes a scheduler for determining (scheduling) a transportformat (a transport block size and a modulation and coding scheme) of anuplink and a downlink, and a resource block to be assigned to the UE100.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the physical layer. Between theRLC layer of the UE 100 and the RLC layer of the eNB 200, user data andcontrol signals are transmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane that handles controlsignals. Between the RRC layer of the UE 100 and the RRC layer of theeNB 200, a control signal (an RRC message) for various types of settingsis transmitted. The RRC layer controls the logical channel, thetransport channel, and the physical channel according to theestablishment, re-establishment, and release of a radio bearer. Whenthere is a connection (an RRC connection) between the RRC of the UE 100and the RRC of the eNB 200, the UE 100 is in an RRC connected mode.Otherwise, the UE 100 is in an RRC idle mode.

An NAS (Non-Access Stratum) layer positioned above the RRC layerperforms session management, mobility management and the like.

FIG. 5 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency Division MultipleAccess) is applied to a downlink, and SC-FDMA (Single Carrier FrequencyDivision Multiple Access) is applied to an uplink, respectively.

As illustrated in FIG. 5, a radio frame is configured by 10 subframesarranged in a time direction. Each subframe is configured by two slotsarranged in the time direction. Each subframe has a length of 1 ms andeach slot has a length of 0.5 ms. Each subframe includes a plurality ofresource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. Each resource block includes a pluralityof subcarriers in the frequency direction. One subcarrier and one symbolform one resource element. Of the radio resources (time and frequencyresources) assigned to the UE 100, a frequency resource can beidentified by a resource block and a time resource can be identified bya subframe (or a slot).

(2) D2D proximity service

The D2D proximity service will be described below. The LTE systemaccording to an embodiment supports the D2D proximity service. The D2Dproximity service is disclosed in Non Patent Literature 1, and anoverview of the D2D proximity service will be here described.

The D2D proximity service (D2D ProSe) is a service that enables directD2D communication to be performed in a synchronous cluster including aplurality of UEs 100 which are synchronized with one another. The D2Dproximity service includes a D2D discovery process (ProSe Discovery) ofdiscovering a nearby UE and D2D communication (ProSe Communication) thatis direct inter-UE communication.

A scenario in which all the UEs 100 constituting the synchronous clusterare positioned within a cell coverage is referred to as “in coverage.” Ascenario in which all the UEs 100 constituting the synchronous clusterare positioned out of the cell coverage is referred to as “out ofcoverage.” A scenario in which some UEs 100 in the synchronous clusterare positioned within the cell coverage, and the remaining UEs 100 arepositioned out of the cell coverage is referred to as “partialcoverage.”

In existing circumstances, the D2D discovery process is assumed to beperformed only within the coverage. Hereinafter, a case in which the D2Ddiscovery process is performed within the coverage is mainly assumed.

In the D2D discovery process, the UE 100 transmits a D2D discoverysignal for discovering a nearby terminal. As a D2D discovery processmethod, there are a first method (Type 1 discovery) in which radioresources that are not uniquely allocated to the UE 100 are used fortransmission of the D2D discovery signal and a second method (Type 2discovery) in which radio resources that are uniquely allocated to eachUE 100 are used for transmission of the D2D discovery signal. In thesecond method, radio resources that are individually orsemi-persistently allocated to each transmission of the D2D discoverysignal are used.

Within the coverage, the eNB 200 functions as a D2D synchronizationsource. The eNB 200 transmits the SIB related to the D2D proximityservice. Hereinafter, such a SIB is referred to as the SIB 19. The SIB19 is a type of system information that is transmitted in a broadcastmanner.

The SIB 19 includes resource pool information indicating a D2D discoveryresource pool used for transmission of the D2D discovery signal in itsown cell. The D2D discovery resource pool may individually include atransmission resource pool and a reception resource pool. The SIB 19includes a frequency list indicating another frequency that is differentfrom a frequency of its own cell but available for the D2D discoveryprocess. The frequency list is used for the D2D discovery process (theinter-frequency discovery) between different frequencies.

(3) Inter-Frequency Discovery

The inter-frequency discovery will be described. FIG. 6 is a diagram fordescribing the inter-frequency discovery. In FIG. 6, the UE 100 is in aconnected mode or an idle mode and selects a cell #1 of the eNB 200 asthe serving cell.

As illustrated in FIG. 6, the eNB 200 transmits the SIB 19 (systeminformation) through the cell #1. As described above, the SIB 19includes the resource pool information of the cell #1 and the frequencylist indicating another frequency available for the D2D discoveryprocess. The SIB 19 may include the resource pool information of aneighboring cell of the same frequency as the frequency of the cell #1.However, it should be noted that the SIB 19 does not include theresource pool information of another frequency different from thefrequency of the cell #1. The UE 100 receives the SIB 19 through thecell #1.

The UE 100 monitors the D2D discovery signal that is transmitted at thefrequency (another frequency) in the frequency list based on thefrequency list included in the SIB 19. The frequency in the frequencylist is different from the frequency of the cell #1, and it is difficultfor the UE 100 to simultaneously perform monitoring of the D2D discoverysignal and downlink cellular communication (communication with the cell#1). Thus, it is desirable that the UE 100 monitor the D2D discoverysignal in a period of time in which the downlink cellular communicationis not performed so that the cellular communication is not interruptedby the monitoring of the D2D discovery signal.

For example, the UE 100 that performs intermittent reception (DRX) canmonitor the D2D discovery signal of another frequency in an OFF periodof time. The OFF period of time is a different period of time from an ONperiod of time in which a PDCCH of the cell #1 (the serving cell) ismonitored. The eNB 200 detects the OFF period of time of the UE 100, anddoes not perform downlink transmission to the UE 100 in the OFF periodof time. However, in this method, when the OFF period of time is short,an opportunity to monitor the D2D discovery signal of another frequencyis small. Thus, it is hard to increase the success rate of theinter-frequency discovery.

In an embodiment, a new timing (a monitoring gap) in which the UE 100monitors the D2D discovery signal of another frequency is introduced.The monitoring gap is allocated from the eNB 200 to the UE 100, and thusthe success rate of the inter-frequency discovery can be increased.

(4) Monitoring Gap Allocation

A monitoring gap allocation according to an embodiment will be describedbelow. FIG. 7 is a diagram for describing a monitoring gap allocationaccording to an embodiment.

As illustrated in FIG. 7, a cell #1 managed by an eNB 200-1 and a cell#2 managed by an eNB 200-2 overlap at least partially. The cell #1belongs to a frequency #1, and the cell #2 belongs to a frequency #2. Inother words, the cell #1 and the cell #2 differ in a frequency.

The cell #1 belongs to a public land mobile network (PLMN) #1, and thecell #2 belongs to a PLMN #2. In other words, the cell #1 and the cell#2 differ in a PLMN. In this case, it should be noted that it isdifficult for the cell #1 and the cell #2 to perform inter-cellcollaboration. In addition, the cell #1 and the cell #2 may not besynchronized with each other.

A UE 100-1 and a UE 100-3 exist in an overlapping region of the cell #1and the cell #2, and select the cell #1 as the serving cell. A UE 100-2exist in the cell #2, and selects the cell #2 as the serving cell.

A method of allocating the monitoring gap in which the UE 100-1 monitorsthe D2D discovery signal transmitted from the UE 100-2 in such anoperation environment will be described.

First, the UE 100-1 receives the SIB 19 transmitted from the eNB 200-1through the cell #1 and decodes the SIB 19. The SIB 19 includes theresource pool information of the cell #1 and the frequency listindicating another frequency available for the D2D discovery process.The UE 100-1 decides to perform the D2D discovery process at anotherfrequency (the frequency of the cell #2) based on the frequency list. Astate in which the UE 100-1 decides to perform the D2D discoveryprocess, and the D2D discovery process does not start yet is referred toas a “state in which it becomes interested in D2D discovery process.”However, a state in which the UE 100-1 is performing the D2D discoveryprocess may be included in the “state in which it becomes interested inD2D discovery process.”

In step S101, the eNB 200-2 transmits the SIB 19 through the cell #2.The SIB 19 includes the resource pool information of the cell #2 and thefrequency list indicating another frequency available for the D2Ddiscovery process. The UE 100-1 that becomes interested in the D2Ddiscovery process at the frequency of the cell #2 receives the SIB 19from the eNB 200-2 through the cell #2 and decodes the SIB 19. Here, itshould be noted that the UE 100-1 receives and decodes the SIB 19 of thecell #2 different from that of the serving cell.

The UE 100-1 transmits a gap allocation request to the eNB 200-1 throughthe cell #1 based on the resource pool information included in the SIB19 of the cell #2 (hereinafter, referred to as “resource poolinformation of the cell #2”).

Firstly, the gap allocation request includes feedback corresponding tothe resource pool information of the cell #2. As a feedback method,there are a first feedback method and a second feedback method.

The first feedback method is a method of feeding back the resource poolinformation of the cell #2 without change. As a result, the eNB 200-1can entirely detect the D2D discovery resource pool of the cell #2.

The second feedback method is a method in which the UE 100-1 decides agap pattern based on the resource pool information of the cell #2, andfeeds back the decided gap pattern (a requested gap pattern).Specifically, the UE 100-1 decides the gap pattern including timings(subframes) included in the D2D discovery resource pool of the cell #2based on the resource pool information.

For example, the requested gap pattern is expressed by periodinformation (discoveryPeriod), offset information(discoveryOffsetIndicator) indicating a start timing of the periodinformation with respect to a timing of the serving cell, bitmapinformation (discoverySubframeBitmap) of a subframe unit indicating thegap pattern, and information (discoveryNumRepetition) indicating thenumber of repetitions of the bitmap information in the periodinformation.

When the UE 100-1 becomes interested in the D2D discovery process at aplurality of frequencies different from the frequency of the cell #1, asum of gap patterns of a plurality of frequencies may be set as therequested gap pattern. Alternatively, a plurality of gap patternscorresponding to the respective frequencies may be set.

FIGS. 8(a) to 8(d) are diagrams for describing an exemplaryconfiguration of the requested gap pattern.

As illustrated in FIG. 8(a), the UE 100-1 detects the D2D discoveryresource pool of the serving cell (the cell #1) belonging to thefrequency #1.

As illustrated in FIGS. 8(b) and 8(c), the UE 100-1 becomes interestedin the D2D discovery process at the frequency #2 and the frequency #3,acquires the SIBs 19 of the frequency #2 and the frequency #3, anddetects the D2D discovery resource pools of the frequency #2 and thefrequency #3.

As illustrated in FIG. 8(d), the UE 100-1 decides a gap pattern obtainedby subtracting the gap pattern of the frequency #1 from a sum of the gappattern of the frequency #2 illustrated in FIG. 8(b) and the gap patternof the frequency #3 illustrated in FIG. 8(c) as the requested gappattern. In the example of FIG. 8(d), the requested gap pattern isexpressed by discoveryPeriod indicating a predetermined duration,discoveryOffsetIndicator indicating an offset of one subframe,discoverySubframeBitmap including a bitmap “1001000110 . . . ”indicating a gap pattern of a subframe unit, and discoveryNumRepetitionindicating a predetermined number of repetitions. In the bitmap, “1”indicates a subframe that constitutes the monitoring gap, and “0”indicates a subframe that does not constitute the monitoring gap.discoveryOffsetIndicator related to the gap pattern preferably has anoffset value starting from SFN=0 of the cell #1.

When the UE 100-1 includes one receiver, in order to have a margin of atime required for frequency switching, a time required for frequencyswitching may be included in the gap pattern as a margin. For example,when one subframe is required as a switching time, one subframe beforeand after the monitoring gap is included in the requested gap pattern aswell.

Secondly, the gap allocation request includes information indicatinganother frequency at which the UE 100-1 becomes interested in the D2Ddiscovery process. In the example of FIGS. 8(a) to 8(d), the UE 100-1includes identification information of the frequency #2 andidentification information of the frequency #3 in the gap allocationrequest.

Thirdly, the gap allocation request may include a tag number associatedwith the SIB 19 which the UE 100-1 acquires at another frequency. Thetag number is a number that is updated with the update of the SIB 19.The tag number is included in a SIB 1 serving as system information usedfor scheduling of the SIB 19. Alternatively, the tag number may beincluded in the SIB 19. The tag number is referred to as“systemInfoValueTag.”

The gap allocation request may be included in D2D indication (ProSeindication) serving as an RRC message for the D2D proximity service.

In step S103, the eNB 200-1 that has received the gap allocation requestfrom the UE 100-1 transmits a gap allocation response to the UE 100-1through the cell #1.

When the first feedback method is applied, the eNB 200-1 decides the gappattern including timings (subframes) included in the D2D discoveryresource pool of the cell #2, and includes the decided gap pattern inthe gap allocation response. As a result, a notification of the gappattern decided by the eNB 200-1 is given to the UE 100-1.

On the other hand, when the second feedback method is applied, the eNB200-1 decides whether or not the requested gap pattern of the UE 100-1is permitted, and includes information (ACK/NACK) about whether or notthe requested gap pattern of the UE 100-1 is permitted in the gapallocation response. When the requested gap pattern of the UE 100-1 isdenied, the eNB 200-1 may revise the requested gap pattern of the UE100-1 and include the revised gap pattern in the gap allocationresponse. The gap allocation response may be an RRC connectionreconfiguration message for reconstituting an RRC setting.

As described above, the eNB 200 allocates the gap pattern specifying atiming at which the UE 100-1 monitors the D2D discovery signaltransmitted from the UE 100-2 at another frequency different from thefrequency of its own cell to the UE 100 based on the gap allocationrequest received from the UE 100-1 connected to its own cell.

Further, when the second feedback method is applied, it is possible toreduce an amount (overhead) of a control signal that is transmitted andreceived by the UE 100-1 and the eNB 200-1 to be smaller than when thefirst feedback method is applied.

In step S104, the UE 100-1 monitors the D2D discovery signal of anotherfrequency at the timing (subframe) set according to the allocated gappattern. Through the monitoring, the UE 100-1 receives the D2D discoverysignal transmitted from the UE 100-2 and discovers the UE 100-2.

Since the eNB 200-1 detects the gap pattern (the monitoring gap) set tothe UE 100-1, it is possible to prevent the downlink signal (forexample, the control signal such as the paging signal or the like) frombeing transmitted to the UE 100-1 in the monitoring gap. Further, whenit is difficult to perform uplink transmission (data or feedback such asHARQ Ack/Nack) during D2D reception, it is possible to preventallocation of uplink transmission or recognize that there is noabnormality (recognize that the inter-frequency discovery is beingperformed) even though it is not transmitted. Thus, the D2D discoveryprocess can be prevented from interrupting the cellular communication.

(5) Overview of Feedback Control

In the operation environment illustrated in FIG. 7, the eNB 200-1 isassumed to further allocate the gap pattern to the UE 100-3.

The D2D discovery resource pool is considered not to dynamically change.For this reason, when the eNB 200-1 accumulates and manages thefeedbacks received from the UEs 100, the necessity of the feedback bythe UE 100 performing the inter-frequency discovery in the cell #1 islow. Particularly, when the first feedback method is applied, if all theUEs 100 performing the inter-frequency discovery feedback the resourcepool information, the overhead is excessively increased.

In this regard, in an embodiment, an increase in the overhead associatedwith the feedback is controlled by enabling the eNB 200-1 to controlwhether or not the feedback is given.

FIG. 9 is a diagram for describing feedback control according to anembodiment.

As illustrated in FIG. 9, in step S21, the eNB 200-1 transmits feedbackcontrol information used for determining whether or not it is necessaryto include the feedback in the gap allocation request to the UE 100-3.As described above, the feedback refers to the resource pool informationin the case of the first feedback method, and refers to the requestedgap pattern in the case of the second feedback method.

The feedback control information is transmitted through broadcasting bythe system information (for example, the SIB 19). Alternatively, thefeedback control information may be transmitted through unicasting byindividual RRC signaling.

In step S22, the UE 100-3 receives the feedback control information. TheUE 100-3 determines whether or not it is necessary to include thefeedback in the gap allocation request based on the feedback controlinformation.

When it is determined to be necessary to include the feedback in the gapallocation request, the UE 100-3 includes the feedback in the gapallocation request to be transmitted to the eNB 200-1. On the otherhand, when it is determined not to be necessary to include the feedbackin the gap allocation request, the UE 100-3 does not include thefeedback in the gap allocation request to be transmitted to the eNB200-1.

As described above, the eNB 200-1 can determine whether or not thefeedback is given, and thus it is possible to appropriately allocate thegap pattern to the UE 100-3 while suppressing the increase in theoverhead associated with the feedback.

(6) Specific Example of Feedback Control

Specific examples of the feedback control will be described below.

(6.1) First Specific Example

The feedback control information includes information indicating whetheror not the feedback is necessary.

The feedback control information may be provided for each frequencyincluded in another frequency (Inter-frequency). For example, the eNB200-1 may transmit the feedback control information indicating “feedbackis necessary” for the frequency #2 and the feedback control informationindicating “feedback is unnecessary” for the frequency #3.

Then, when the UE 100-3 becomes interested in the D2D discovery processat the frequency #2, the UE 100-3 included the feedback in the gapallocation request to be transmitted to the eNB 200-1. Further, when theUE 100-3 becomes interested in the D2D discovery process at thefrequency #3, the UE 100-3 includes the feedback in the gap allocationrequest to be transmitted to the eNB 200-1.

(6.2) Second Specific Example

The feedback control information includes the tag number(systemInfoValueTag) of the system information (the SIB 19) acquired bythe eNB 200-1 so that the UE 100 determines whether or not the feedbackis necessary.

As described above, the gap allocation request includes the tag numberassociated with the SIB 19 which the UE 100-1 acquires at anotherfrequency. Thus, the eNB 200-1 includes the tag number corresponding tothe D2D discovery resource pool detected by the eNB 200-1 in thefeedback control information, and transmits the resulting feedbackcontrol information.

The feedback control information may be provided for each frequencyincluded in another frequency (Inter-frequency). For example, when theeNB 200-1 detects the D2D discovery resource pool of the SIB 19 of a tagnumber #5 for the frequency #2, the eNB 200-1 transmits the feedbackcontrol information indicating that the feedback corresponding to theSIB 19 of the tag number #5 for the frequency #2 is unnecessary.

The UE 100-3 does not acquire the SIB 19 of the tag number #5 for thefrequency #2 from the eNB 200-2 (the cell #2). Alternatively, althoughthe UE 100-3 acquires the SIB 19 of the tag number #5 for the frequency#2 from the eNB 200-2, the UE 100-3 does not include the feedback in thegap allocation request to be transmitted to the eNB 200-1. However, whenthe UE 100-3 acquires the SIB 19 of a tag number #6 for the frequency #2from the eNB 200-2, the UE 100-3 includes the feedback in the gapallocation request to be transmitted to the eNB 200-1.

(6.3) Third Specific Example

When the second feedback method is applied, the feedback controlinformation may include information indicating the gap pattern acquiredby the eNB 200-1 so that the UE 100 determines whether or not thefeedback is necessary. As described above, the gap pattern can beexpressed by discoveryPeriod, discovery OffsetIndicator, discoverySubframeBitmap, and discoveryNumRepetition.

The feedback control information may be provided for each frequencyincluded in another frequency (Inter-frequency). For example, the eNB200-1 transmits the feedback control information indicating that thefeedback of a specific gap pattern is unnecessary for the frequency #2.The UE 100-3 does not include the feedback of the specific gap patternin the gap allocation request.

(6.4) Fourth Specific Example

The feedback control information includes information indicating a validperiod of time of the feedback control information. For example, thevalid period of time can be expressed by a coordinated universal time(UTC).

It is desirable that the information indicating the valid period of timebe included in the feedback control information of the first to thirdspecific examples. It is desirable that the valid period of time be setas a period of time equal to an update period of the SIB 19.

When it is within the valid period of time, the UE 100-3 that hasreceived the feedback control information gives the feedback accordingto the feedback control information. However, after the valid period oftime elapses, the UE 100-3 may not follow the feedback controlinformation.

Other Embodiments

In the above embodiment, the example in which the SIB related to the D2Dproximity service is the SIB 19 has been described. However, theinformation related to the D2D proximity service may be carried througha SIB (a SIBx) other than the SIB 19.

In the above embodiment, the feedback and the feedback control of thefrequency units have been described, but the feedback and the feedbackcontrol may be performed in more detailed units (for example, cellunits) than the frequency units. In this case, in addition to or insteadof a frequency identifier, a cell identifier is transmitted andreceived.

In the above embodiment, the D2D discovery process (Inter-PLMNDiscovery) when the PLMNs are different has been described, but thepresent invention is not limited to this example. The present inventioncan be applied even to the case of the D2D discovery process (Intra-PLMN& Inter-freq. Discovery) when the PLMNs are the same.

In the above embodiment, the eNB 200-1 acquires the discovery resourceinformation of another PLMN from the UE 100, but the present inventionis not limited to this example. For example, the eNB 200-1 may acquirethe discovery resource information from the eNB 200-2 through the X2interface.

In the above embodiment, the feedback control of FIG. 9 is control as towhether or not the feedback is included in the gap allocation request(for example, ProSe indication). However, when a feedback-dedicatedmessage (for example, UE Assistance Information) is used, the controlmay be applied to the dedicated message.

In the above embodiment, the D2D discovery process (ProSe Discovery) hasbeen described, but it will be appreciated that the present inventioncan be applied to the D2D communication (ProSe Communication). In otherwords, the “D2D discovery process” of the above embodiment may bereplaced with the “D2D communication,” and the “D2D discovery signal”may be replaced with the “D2D communication signal.”

In the above embodiment, the LTE system has been described as an exampleof the mobile communication system, but the present invention is notlimited to the LTE system and can be applied to other systems than theLTE system.

[Additional Statement]

1. Introduction

The introduction of inter-PLMN discovery was agreed in RAN2#87;

Agreements

-   1 RAN2 aims to support of Inter-Frequency and Inter-PLMN discovery    for monitoring UEs will be introduced.-   2 An eNB may provide in SIB a list of (intra-PLMN-inter-frequency    and/or inter-PLMN-inter-frequency) carriers (possibly with the    corresponding PLMN ID) on which the UE may aim to receive ProSe    discovery signals.-    A cell does not provide detailed ProSe configuration (SIB18) for    other carriers. If a UE wants to receive ProSe discovery signals on    another carrier, it needs to read SIB18 (and other relevant SIB)    from there.    [. . . ]-   3 UEs transmit ProSe discovery signals only on their serving cell    (if authorized by the NW).-   4 Intra- and inter-frequency (and inter-PLMN) ProSe reception does    not affect Uu reception (e.g. UEs use DRX occasions in IDLE and    CONNECTED to perform ProSe discovery reception or it uses a second    RX chain if available). The UE shall not create autonomous gaps.-    If the UE has to obtain ProSe discovery (2a) configuration from the    SIB of an inter-frequency cell, this does not affect the UE's Uu    reception on the serving cell(s).-   5 An RRC CONNECTED UE interested (or no longer interested) in intra-    or inter frequency ProSe discovery reception indicates this by    sending a “ProSe indication” to the eNB (further restrictions to be    discussed).

In following RAN2#87bis, the open issues on D2D discovery were capturedbut some of them were not discussed;

Open issues[. . . ]

3) Need for additional gaps (besides DRX occasions) in which the UE cantune to other frequencies for receiving ProSe discovery signals? If so,should those be autonomous or configured? If configured, how does theeNB where to provide them?

4) Further need to clarify prioritization between Uu and PC5transmission/reception?

In this contribution, the open issues are discussed to supportinter-frequency/inter-PLMN discovery in Rel-12.

2. Needs for Additional Gaps for Discovery Monitoring

RAN1 had performed evaluation of D2D discovery in the study phase andthe result was captured in the TR. According to the system levelsimulation in FIG. 1, the discovery performance, as measured by thenumber of devices discovered, is dependent on how many periods the UEcan announce/monitor discovery signals. However, even if sufficientdiscovery periods are provided by the network, the number of devicesdiscovered is contingent on the opportunities for the UEs toannounce/monitor during the discovery periods. For intra-frequencydiscovery, since the serving cell provides the reception pools of boththe serving cell and the neighbour cells, the discovery performance isguaranteed according to the rule agreed in RAN1#78bis as follows;

Agreement:

-   -   For FDD carriers:        -   At least for UEs with a single Rx chain (FFS subject to the            UE capability discussion whether this also applies for UEs            with a shared D2D/cellular Rx chain), a UE that is receiving            D2D discovery signals on an UL carrier is not expected to            read DL signals on the DL carrier paired to such UL carrier            during the subframes belonging to the D2D discovery pools on            that UL carrier as well as one subframe preceding and            following these subframes            -   The discovery pools are configured by the eNB by                broadcast or UE-specific signaling                -   FFS: For RRC_CONNECTED UEs, 1 bit may be signalled                    using RRC signaling indicating whether this rule                    applies or not (on a per UE basis)        -   Cellular measurement gaps subframes are excluded from this            rule        -   Paging reception is prioritized over D2D reception    -   For TDD carriers:        -   A UE configured by the eNB to monitor D2D on a certain            carrier is expected to read DL signals on that carrier            according to legacy procedures.            And for inter-frequency or inter-PLMN discovery, the UE,            with a single Rx chain, may use DRX occasions to avoid any            degradation to Uu reception, as depicted in FIG. 2. As            suggested, ProSe discovery using only DRX occasion may            result in degradations of the discovery performances, i.e.            best-effort discovery and the number of devices discovered            will be significantly limited even if there were sufficient            discovery periods.

-   Observation 1: If only existing DRX occasions are used, discovery    opportunities may be severely limited.

To ensure moderate performance for inter-frequency and inter-PLMNdiscovery and to realize some of the performance gains from thediscovery periods provided by the network, additional gaps for discoverymonitoring for should be introduced. The gaps may be based on thesubframes belonging to the D2D discovery pool for the specific ULcarrier based on RAN1's agreements above.

-   Proposal 1: Gaps for discovery monitoring should be introduced in    addition to the existing DRX occasion.

3. Additional Gaps 3.1. Working Assumptions

To form a common view as working assumption, the knowledge of theserving cell should be clarified.

With intra-PLMN discovery, it may be assumed that the serving cell hasknowledge of the detailed ProSe discovery information of its neighbourcells although it's already agreed that the serving cell does notprovide detailed ProSe discovery information for inter-frequencyneighbour cells in SIB19. It's up to OAM or deployment policy whetherthe eNB is configured with such information.

However, we believe such tight coordination among networks should not beextended to inter-PLMN discovery, as discussed in RAN2#87;

-   [. . . ] Ericsson is just concerned that any solution that we do for    inter-PLMN support should be simple. ZTE agrees with Ericsson.    [. . . ]-   Vodafone thinks that it will be difficult to transmit in the SIB of    a carrier in one PLMN about ProSe discovery on another PLMN is    challenging and could certainly not be dynamic. DT does not expect    it to be dynamic. Ericsson agrees with Vodafone.-   Confirmation 1: As a working assumption, tight coordination among    PLMNs should not be assumed, while it may be assumed for intra-PLMN    case.

According to the working assumption in Confirmation 1, OAM may be ableto provide the necessary coordination among inter-frequency, intra-PLMNcells such that the serving cell would be able to configure the UE withappropriate gaps, e.g. DRX configuration. However, for the inter-PLMNscenario, the situation is different and no coordination among cellsbelonging to different PLMNs may be assumed. Therefore, the serving cellshould have a means to obtain the information from the UE as suggested,since the UE may have already obtained the information directly from theother PLMN, e.g. during DRX occasion.

-   Proposal 2: There should be a means for the serving cell to obtain    detailed ProSe discovery information from the UE.

If Proposal 2 is agreeable, RAN2 should also consider the control forthe overhead associated with the transfer of detailed ProSe discoveryinformation from the UE to the serving cell. If the serving cell wereable obtain detailed ProSe discovery information through OAM, then itisn't necessary for the UE to provide such information to the servingcell. Additionally, if the serving cell already obtained suchinformation from a UE it won't be necessary for other UEs to provide thesame information, as long as the information has the same contents.Therefore, the serving cell should indicate in SIB or dedicatedsignalling whether the UE should provide the detailed ProSe informationfrom inter-frequency neighbour cells.

-   Proposal 3: The serving cell should have a means to indicate in SIB    or dedicated signalling (possibly for each frequency carrier listed    in SIB19) whether the serving cell has already acquired all the    inter-frequency neighbour cell information needed for assigning    discovery gaps to the UE.

3.2. Additional Gap Alternatives

If Proposal 1: is agreeable, additional gap alternatives should bediscussed. The possible alternatives listed below were previouslyprovided,

-   ALT 1: Reuse the existing measurement gap and Option 1).-   ALT 2: Autonomous gap under permission of the serving cell (Solution    2 or Option 2).-   ALT 3: New discovery gap configured by the serving cell    (“pre-configured gap pattern in Solution 1 or “new gap design” of    Option 3).-   ALT 4: New discovery gap configured by the serving cell, which is    based on a gap pattern requested by the UE (Option 2).

With ALT 1, the existing measurement gap may be a mismatch with thecomplex resource pool pattern and may not ensure reasonable discoveryperformance as described in Observation 1. The existing measurement gapis fixed at 6 subframes while the discovery period is configurable from32-1024 radio frames. In addition, it may be necessary to clarify in thespecification when the existing gap for inter-frequency measurements maybe reused for discovery monitoring. Based on the rule, cellularmeasurement gaps are excluded for use in ProSe discovery. If theextended DRX configuration could be reused for discovery monitoring, thedefinition of the Power Preference Indication should be extended toallow its use for ProSe discovery. But even with such an extension, itmay still not be possible to cover all the necessary discovery periodswithout further coordination.

Regarding ALT 2, although it was already agreed at RAN2#87 that the UEshall not create autonomous gaps, it may be useful as long as it'sallowed by the serving cell, especially if the UE can obtain thepatterns of resource pools of other carrier by decoding SIB19s aspointed out. This is particularly beneficial in the inter-PLMN scenario,since it is assumed that the serving cell has no knowledge of detailedProSe discovery information belonging to inter-PLMN cells.

ALT 3 may work well in the intra-PLMN case; however, it's questionableif it will also work for inter-PLMN case due to lack of knowledge in theserving cell, as mentioned above.

ALT 4 may be considered as a harmonized solution between ALT 2 and ALT 3and it can also provide a unified mechanism for support of both intra-and inter-PLMN discovery. Therefore, ALT 4 should be introduced as thebaseline mechanism for the additional gap for discovery monitoring.

-   Proposal 4: The serving cell should configure the UE with gaps for    inter-frequency and/or inter-PLMN discovery monitoring, which may be    based on a gap pattern requested by the UE.

4. Discovery Monitoring Gap Details

4.1. Request of Gap Assignment from the UE

Assuming the UE can obtain the resource pool configurations of interestdirectly from the SIB of other carriers including other PLMNs, the UEcould inform the serving cell of the desired gap patterns for discoverymonitoring. The gap pattern should be based on the subset of the RRCparameter defined by RAN1, i.e., discoveryPeriod,discoveryOffsetIndicator, discoverySubframeBitmap anddiscoveryNumRepetition for the serving cell and neighbour cells.Therefore, the IE structure should be common with the parameters.

-   Proposal 5: The gap pattern requested by the UE should be based on    the subset of the RRC parameters defined by RAN1.

Following the current agreements, the resource pool offset, which isdescribed by discoveryOffsetIndicator, should be provided with respectto SFN=0 of the serving cell as one value.

-   Proposal 6: discoveryOffsetIndicator for the gap pattern in the    request sent from the UE should be provided with respect to SFN=0 of    the serving cell as one value.

The issue to be discussed is whether the request contains only onepattern or multiple patterns, i.e., an integrated pattern for all othercarriers or separated patterns for each carrier. Although the separatedpatterns may allow more flexibility for the gap assignment performed inthe serving cell, from overhead reduction perspective it's preferred toinform of an integrated pattern in the request.

-   Proposal 7: A single pattern which integrates all resource pool    patterns of interest should be informed in the request from the UE.

Obviously, the request comes up with the UE's interest of discoverymonitoring. Therefore, it's quite natural to include the request of gapassignment in the ProSe Indication. If Proposal 3: is acceptable, it maybe also under control of the serving cell whether the UE includes thegap pattern in the request.

-   Proposal 8: The ProSe Indication may include the request of gap    assignment with required gap pattern.

4.2. Gap Assignment as Response to the UE

Upon reception of the ProSe Indication which includes the request of gapassignment, it is up to the serving cell to decide whether to use the UErequested gap pattern for gap assignment through dedicated signalling.

-   Proposal 9: Upon reception of the ProSe Indication which includes    the request for gap assignment, the serving cell may configure the    UE with acceptable gap pattern using dedicated signalling.

5. Conclusion

In this paper, the necessity of additional gaps for discovery monitoringis discussed. The alternatives for the gap assignment mechanism areintroduced and the signalling details are considered. Additionalcontrols for overhead reduction are provided. RAN2 is kindly asked totake into account the observation and proposals below.

-   Observation 1: If only existing DRX occasions are used, discovery    opportunities may be severely limited.-   Proposal 1: Gaps for discovery monitoring should be introduced in    addition to the existing DRX occasion.-   Confirmation 1: As a working assumption, tight coordination among    PLMNs should not be assumed, while it may be assumed for intra-PLMN    case.-   Proposal 2: There should be a means for the serving cell to obtain    detailed ProSe discovery information from the UE.-   Proposal 3: The serving cell should have a means to indicate in SIB    or dedicated signalling (possibly for each frequency carrier listed    in SIB19) whether the serving cell has already acquired all the    inter-frequency neighbour cell information needed for assigning    discovery gaps to the UE.-   Proposal 4: The serving cell should configure the UE with gaps for    inter-frequency and/or inter-PLMN discovery monitoring, which may be    based on a gap pattern requested by the UE.-   Proposal 5: The gap pattern requested by the UE should be based on    the subset of the RRC parameters defined by RAN1.-   Proposal 6: discoveryOffsetIndicator for the gap pattern in the    request sent from the UE should be provided with respect to SFN=0 of    the serving cell as one value.-   Proposal 7: A single pattern which integrates all resource pool    patterns of interest should be informed in the request from the UE.-   Proposal 8: The ProSe Indication may include the request of gap    assignment with required gap pattern.-   Proposal 9: Upon reception of the ProSe Indication which includes    the request for gap assignment, the serving cell may configure the    UE with acceptable gap pattern using dedicated signalling.

1. A base station that allocates a gap pattern to a user terminalconnected to an own cell based on a message received from the userterminal, the gap pattern defines timings in which the user terminalshould monitor D2D signals transmitted from other user terminals atdifferent frequencies than a frequency of the own cell, comprising: atransmitter that transmits feedback control information to the userterminal, the feedback control information used to determine whether ornot it is necessary for the user terminal to include, in the message,feedback corresponding to system information that is received by theuser terminal at the different frequencies.
 2. The base stationaccording to claim 1, wherein the system information includes resourcepool information indicating a D2D resource pool used for transmission ofthe D2D signals at the different frequencies, and the feedback is arequested gap pattern that is decided by the user terminal based on theresource pool information, or the resource pool information.
 3. The basestation according to any one of claims 1 and 2, wherein the feedbackcontrol information includes information indicating whether or not thefeedback is necessary.
 4. The base station according to any one ofclaims 1 and 2, wherein the system information includes a tag numberthat is updated with an update of the system information, and thefeedback control information includes the tag number of the systeminformation acquired by the base station in order for the user terminalto determine whether the feedback is necessary.
 5. The base stationaccording to any one of claims 1 and 2, wherein the feedback controlinformation includes information indicating a gap pattern acquired bythe base station in order for the user terminal to determine whether thefeedback is necessary.
 6. The base station according to any one ofclaims 1 to 5, wherein the feedback control information is provided foreach frequency included in the different frequencies.
 7. The basestation according to any one of claims 1 to 6, wherein the feedbackcontrol information includes information indicating a valid period oftime of the feedback control information.
 8. A user terminal to which agap pattern is allocated by a serving cell based on a messagetransmitted to the serving cell, the gap pattern defines timings inwhich the user terminal should monitor D2D signals transmitted fromother user terminals at different frequencies than a frequency of theserving cell, comprising: a receiver that receives feedback controlinformation from the serving cell, the feedback control information usedto determine whether or not it is necessary for the user terminal toinclude, in the message, feedback corresponding to system informationthat is received by the user terminal at the different frequencies. 9.The user terminal according to claim 8, wherein the system informationincludes resource pool information indicating a D2D resource pool usedfor transmission of the D2D signals at the different frequencies, andthe feedback is a requested gap pattern that is decided by the userterminal based on the resource pool information, or the resource poolinformation.
 10. The user terminal according to any one of claims 8 and9, wherein the feedback control information includes informationindicating whether or not the feedback is necessary.
 11. The userterminal according to any one of claims 8 and 9, wherein the systeminformation includes a tag number that is updated with an update of thesystem information, and the feedback control information includes thetag number of the system information acquired by the base station inorder for the user terminal to determine whether the feedback isnecessary.
 12. The user terminal according to any one of claims 8 and 9,wherein the feedback control information includes information indicatinga gap pattern acquired by the base station in order for the userterminal to determine whether the feedback is necessary.
 13. The userterminal according to any one of claims 8 to 12, wherein the feedbackcontrol information is provided for each frequency included in thedifferent frequencies.
 14. The user terminal according to any one ofclaims 8 to 13, wherein the feedback control information includesinformation indicating a valid period of time of the feedback controlinformation.